<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>变量</title>

    <script>

        var a = 3;
        alert(a);
        document.write(a+"========="+typeof(a)+"<br>")
        a="bbb"
        document.write(a+"========="+typeof(a)+"<br>")

    </script>
</head>
<body>

</body>
</html>